EP0206926B1 - Polymeric dielectric material with a high dielectric permittivity - Google Patents

Polymeric dielectric material with a high dielectric permittivity Download PDF

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Publication number
EP0206926B1
EP0206926B1 EP86401317A EP86401317A EP0206926B1 EP 0206926 B1 EP0206926 B1 EP 0206926B1 EP 86401317 A EP86401317 A EP 86401317A EP 86401317 A EP86401317 A EP 86401317A EP 0206926 B1 EP0206926 B1 EP 0206926B1
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mol
vinylidene fluoride
weight
trifluoroethylene
copolymer
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German (de)
French (fr)
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EP0206926A1 (en
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Dominique Broussoux
François Micheron
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
    • H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds
    • H01B3/445—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds from vinylfluorides or other fluoroethylenic compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/002—Details
    • H01G4/018—Dielectrics
    • H01G4/06—Solid dielectrics
    • H01G4/14—Organic dielectrics
    • H01G4/18—Organic dielectrics of synthetic material, e.g. derivatives of cellulose
    • H01G4/186—Organic dielectrics of synthetic material, e.g. derivatives of cellulose halogenated

Definitions

  • the present invention relates to dielectric materials formed from polymers and which have a high dielectric permittivity.
  • PVF 2 polyvinylidene fluoride
  • a dielectric material often used for the manufacture of capacitors is polyvinylidene fluoride (PVF 2 ) which has interesting dielectric properties. It can be obtained in the form of thin films. However, due to technological difficulties, it is difficult to obtain films with a thickness of less than 5 mm. This imposes limitations on the volume capacity of the PVF 2 capacitors since this capacity is inversely proportional to the square of the thickness of the dielectric. We have therefore sought to improve, by different treatments, the dielectric permittivity values of PVF 2 for ranges of temperatures and frequencies as wide as possible. It is also sought to bring the range of optimal operating temperatures closer to ambient temperature.
  • PVF 2 polyvinylidene fluoride
  • Uniaxial or biaxal mechanical stretching increases the value of the permittivity or dielectric constant by approximately 20%.
  • the relative dielectric constant then passes for PVF 2 from 10 to 12.
  • the stretching induced by rolling makes it possible to obtain values between 13 and 15.
  • copolymers rather than the homopolymers, for example the copolymer of vinylidene fluoride and of trifluoroethylene denoted P (VF 2 -TrFE) or also P (VF 2 -VF 3 ).
  • Dielectric properties of such a copolymer are described in the articles CHEMICAL ABSTRACTS, vol. 99, no. 18, October 31, 1983, page 24, abstract no. 140761t, Columbus, Ohio, US; N. KOIZUMI et al .: "Dielectric behavior of copolymers of vinylidene fluoride and trifluoroethylene", and CHEMICAL ABSTRACTS, vol. 99, no. 26, 26 December 1983, page 23, abstract no.
  • terpolymers have appeared, for example the terpolymer of vinylidene fluoride, trifluoroethylene and hexafluoropropene denoted P (VF 2 -TrFE-HFP) or the terpolymer of vinylidene fluoride, tifluoroethylene and trifluorochloroethylene denoted P (VF 2 -TrFE-TrFCIE).
  • P VF 2 -TrFE-HFP
  • P terpolymer of vinylidene fluoride, tifluoroethylene and trifluorochloroethylene
  • the invention provides alloys of ferroelectric polymers at different Curie temperatures, these alloys making it possible to optimize the dielectric properties over a wide range of temperatures and frequencies. These alloys can be produced on the basis of copolymers, on the basis of a homopolymer and on one or more copolymers or else on the basis of terpolymers.
  • the subject of the invention is therefore a dielectric material with a high dielectric constant based on ferroelectric polymers of the vinylidene fluoride copolymer and terpolymer type, characterized in that it consists of an alloy of ferroelectric polymers at different Curie temperatures.
  • the ferroelectric polymers can be copolymers of vinylidene fluoride and of trifluoroethylene P (VF 2 -VF 3 ).
  • the alloy can comprise two or three copolymers of this type.
  • the alloy can also be produced from a homopolymer such as PVF 2 and a copolymer such as P (VF 2 -VF 3 ).
  • Ferroelectric polymers can be terpolymers, which has the advantage of enlarging the zone with a high dielectric constant when the temperature varies.
  • the alloys can be obtained by mixing two terpolymers or by mixing a terpolymer with a copolymer.
  • polymer will be understood broadly, that is to say encompassing copolymers and terpolymers.
  • the various alloys will be produced by mixing in the molten phase of the various components on a mixer with heated rollers for a temperature of approximately 200 ° C.
  • the mixtures are then pressed in the form of thin films from 100 to 120 ⁇ m thick by compression at a temperature of around 180 ° C and cooled by quenching in water to limit crystallization.
  • the samples are covered with metallizations, for example aluminum, on their main faces in order to be able to measure their dielectric constant E r and their loss factor tg8.
  • the measurements will be made for a frequency of 100 Hz and over a temperature range varying from -10 ° C to 140 ° C.
  • FIG. 1 is a diagram showing the evolution of the dielectric constant ⁇ r as a function of the temperature expressed in degrees Celsius for various polymers of the known art. These are copolymers of vinylidene fluoride and trifluoroethylene, ie P (VF 2 -VF 3 ) for different compositions.
  • Curve 1 relates to a copolymer noted 70/30, that is to say where the proportion of vinylidene fluoride is involved for 70% in molar proportion of constituents and trifluoroethylene 30%.
  • Curve 2 relates to the same type of copolymer but in a 60/40 proportion.
  • curve 3 relates to a composition of 50/50 proportion.
  • these copolymers exhibit a phase transition of the ferroelectric type at a temperature above ambient temperature and which is a function of the proportions of its constituents. This transition gives rise to a maximum of the dielectric constant ⁇ r which is relatively high (around 40). This transition is accompanied by a change in crystal structure from the polar phase to the non-polar phase. It will be assumed that the maximum dielectric constant corresponds to the Curie temperature.
  • the maximum dielectric constant is located at a relatively high temperature (80 ° C. for the 50/50 composition) and that this maximum only exists for a range of temperatures. quite limited.
  • the dielectric constant decreases rapidly when the temperature changes from the Curie temperature to the ambient temperature.
  • the 60/40 composition goes from about 42 for 100 ° C to about 10 for 20 ° C
  • curve 4 represents the variation of sr as a function of the temperature in the case of polyvinylidene fluoride. It is therefore found that it is possible to substantially increase the dielectric constant thanks to the copolymers but for high temperatures and for restricted temperature ranges.
  • FIG. 2 is a diagram representing the variation of the dielectric constant ⁇ r with the temperature for alloys according to the invention. These are alloys between copolymers of vinylidene fluoride and trifluoroethylene of different concentrations. Alloy A, corresponding to curve 5, contains 50% by weight of a 60/40 composition and 50% of a 70/30 composition. This alloy has a plateau in dielectric behavior with er of the order of 40 from 110 ° C while this value is only from 10 to 25 ° C. The amplitude of the plateau varies only by a few units in a range of temperatures of around forty degrees. This is an interesting characteristic although the plateau occurs at relatively high temperatures.
  • Alloy B corresponding to curve 6, contains 70% by weight of a 50/50 composition and 30% of a 60/40 composition. This alloy has, around 70 ° C, a maximum of 45 to er. The constant then decreases to 30 for a temperature of the order of 120 ° C. The maximum dielectric constant is high for an average temperature but the plate is still quite narrow.
  • the loss factor is less than 0.03 up to 90 ° C.
  • FIG. 3 is a diagram representing the variation of the dielectric constant er with the temperature for other alloys according to the invention. These are alloys produced from three copolymers of vinylidene fluoride and ethylene trifluoride of compositions 50/50, 60/40 and 70/30 taken in different proportions.
  • Alloy C corresponding to curve 7, has an equal proportion by weight for the three compositions.
  • Alloy D corresponding to curve 8 has a proportion by weight of 45% for the composition 50/50, 35% for the composition 60/40 and 20% for the composition 70/30.
  • the plateau has a fairly constant value ( ⁇ r between 35 and 40) for a wide range of temperatures (between 75 and 140 ° C). It is the low percentage of the composition 70/30 in the alloy D (see curve 8) which causes a drop in the dielectric constant for temperatures above 105 ° C.
  • the dielectric losses are less than 0.04 up to 110 ° C.
  • FIG. 4 is a diagram representing the exothermic heat flow FCE for the alloy C.
  • the curve 9 represents the variation of dielectric constant sr as a function of the temperature. It corresponds to curve 7 in FIG. 3.
  • Curve 10 represents the exothermic heat flow of this alloy as a function of the temperature. The measurement of this heat flux was carried out by differential thermal analysis or DSC according to Anglo-Saxon terminology (Differential Scanning Calorimetry). Curve 10 presents, for the temperature range corresponding to the plateau of curve 9, a trough where several significant temperatures can be noted. The three temperatures Tc i , Tc 2 and Tc 3 are thus noted. The first two are clearly visible on curve 10 since they correspond to minimum heat fluxes. The third corresponds to an inflection point on curve 10.
  • Tci corresponds to the Curie temperature of the composition 50/50
  • Tc3 corresponds to the Curie temperature of the composition 70/30
  • Tc 2 corresponds to the Curie temperature of the composition 60/40. So we can plan that the width of the plate with a dielectric constant which is substantially constant with the temperature will depend on the greater or lesser difference between the Curie temperatures of the different compositions. So that the plateau approaches the ambient temperature, it will therefore be necessary for the Curie temperature of one of the constituents to approach it.
  • FIG. 5 is a diagram representing the variation of the dielectric constant er with the temperature for other alloys according to the invention.
  • These are alloys made from the PVF 2 homopolymer and copolymers of vinylidene fluoride and trifluoroethylene. These alloys can be represented by the notation: PVF 2 + P (VF 2 NF 3 ).
  • the type of copolymer (60/40 or 70/30 for example) used in the mixture is decisive for the temperature positioning of the plate and for the value of er on this plate.
  • the alloy E is represented in FIG. 5 by curve 11.
  • Alloy F composed of 60% by weight of PVF 2 and 40% of a 70/30 copolymer has a maximum dielectric constant (around 30) from 110 ° C (see curve 12).
  • FIG. 6 is a diagram representing the variation of the electrical constant ⁇ r with the temperature in the case of terpolymers.
  • Curve 13 relates to a terpolymer T i of trifluoroethylene, vinylidene fluoride and hexafluoropropene HFP which will be denoted P (VF 3 - VF 2 - HFP) and the proportions of which in moles in the mixture are respectively 35, 60 and 5%.
  • Curves 14 and 15 relate to terpolymers (respectively T 2 and Ts) of trifluoroethylene, vinylidene fluoride and trifluorochloroethylene which will be denoted P (VF 3 - VF 2 - TrFCIE).
  • FIG. 7 is a diagram representing the variation of the dielectric constant er with the temperature in the case of alloys of terpolymers together or with a copolymer.
  • Alloy H is formed by 30% by weight of T i and 70% by T 2 and corresponds to curve 17. This curve has an extended temperature plateau (between 60 and 130 ° C), of high value and relatively constant ( E r from 45 to 50). Under these conditions, this alloy is particularly advantageous.
  • the alloy is formed from 70% by weight of terpolymer T 3 and 30% of copolymer VF 2 - VFs of proportions 60/40 (60% by weight of VF 2 for 40% by weight of VF s ).
  • This alloy corresponds to curve 18.
  • This curve does not have an extended plateau, but alloy I makes it possible to obtain a material with a dielectric constant of between 20 and 30 for a range of temperatures ranging from 20 to 100 °. C and the maximum of which is around 80 ° C.
  • the present invention is not limited to the examples cited above. It applies to all ferroelectric polymer alloys.

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Description

La présente invention concerne les matériaux diélectriques formés à partir de polymères et qui présentent une permittivité diélectrique élevée.The present invention relates to dielectric materials formed from polymers and which have a high dielectric permittivity.

Un matériau diélectrique souvent employé pour la fabrication de condensateurs est le polyfluorure de vinylidène (PVF2) qui possède d'intéressantes propriétés diélectriques. Il peut être obtenu sous forme de films minces. Toutefois, du fait de difficultés technologiques, il est difficile d'obtenir des films d'épaisseur inférieure à 5 mm. Ceci impose des limitations pour la capacité volumique des condensateurs en PVF2 puisque cette capacité est inversement proportionnelle au carré de l'épaisseur du diélectrique. On a donc cherché à améliorer, par différents traitements, les valeurs de permittivité diélectrique du PVF2 pour des gammes de températures et de fréquences aussi étendues que possible. On cherche aussi à ce que la gamme de températures d'utilisation optimale se rapproche de température ambiante.A dielectric material often used for the manufacture of capacitors is polyvinylidene fluoride (PVF 2 ) which has interesting dielectric properties. It can be obtained in the form of thin films. However, due to technological difficulties, it is difficult to obtain films with a thickness of less than 5 mm. This imposes limitations on the volume capacity of the PVF 2 capacitors since this capacity is inversely proportional to the square of the thickness of the dielectric. We have therefore sought to improve, by different treatments, the dielectric permittivity values of PVF 2 for ranges of temperatures and frequencies as wide as possible. It is also sought to bring the range of optimal operating temperatures closer to ambient temperature.

L'étirement mécanique uniaxial ou biaxal permet d'accroître la valeur de la permittivité ou constante diélectrique d'environ 20%. La constante diélectrique relative passe alors pour le PVF2 de 10 à 12. L'étirement induit par laminage permet d'obtenir des valeurs comprises entre 13 et 15.Uniaxial or biaxal mechanical stretching increases the value of the permittivity or dielectric constant by approximately 20%. The relative dielectric constant then passes for PVF 2 from 10 to 12. The stretching induced by rolling makes it possible to obtain values between 13 and 15.

Une autre solution consiste à mélanger le PVF2 avec des poudres ferroélectriques à constantes diélectriques élevées (comprises entre 1000 et 2000). Cette technique, apparue comme un moyen simple et efficace d'augmenter la valeur de la constante eu diélectrique jusqu'aux environs de 40 ou 50, a l'inconvénient majeur d'interdire définitivement l'obtention de films d'épaisseur inférieure à 50 µm.Another solution consists in mixing PVF 2 with ferroelectric powders with high dielectric constants (between 1000 and 2000). This technique, which appeared as a simple and effective means of increasing the value of the dielectric constant to around 40 or 50, has the major drawback of definitively prohibiting the obtaining of films with a thickness of less than 50 μm. .

Une autre possibilité consiste à utiliser les copolymères plutôt que les homopolymères, par exemple le copolymère de fluorure de vinylidène et de trifluoroéthylène noté P(VF2-TrFE) ou encore P(VF2-VF3). Des propriétés diélectriques d'un tel copolymère sont décrites dans les articles CHEMICAL ABSTRACTS, vol. 99, no. 18, 31 octobre 1983, page 24, résumé no. 140761t, Columbus, Ohio, US; N. KOIZUMI et al.: "Dielectric behavior of copolymers of vinylidene fluoride and trifluoroethylene", et CHEMICAL ABSTRACTS, vol. 99, no. 26, 26 décembre 1983, page 23, résumé no. 213226j, Columbus, Ohio, US; K. KIMURA et al.: "Ferroelectric properties of vinylidene fluoride-trifluoroethylene copolymer thin films". Ce copolymère a la particularité de présenter une transition de phase de type ferroélectrique à une température supérieure à la température ambiante et qui est fonction du rapport VF2NF3. Néanmoins, le domaine de températures où la constante diélectrique est élevée (er entre 40 et 50) est limité.Another possibility consists in using the copolymers rather than the homopolymers, for example the copolymer of vinylidene fluoride and of trifluoroethylene denoted P (VF 2 -TrFE) or also P (VF 2 -VF 3 ). Dielectric properties of such a copolymer are described in the articles CHEMICAL ABSTRACTS, vol. 99, no. 18, October 31, 1983, page 24, abstract no. 140761t, Columbus, Ohio, US; N. KOIZUMI et al .: "Dielectric behavior of copolymers of vinylidene fluoride and trifluoroethylene", and CHEMICAL ABSTRACTS, vol. 99, no. 26, 26 December 1983, page 23, abstract no. 213226j, Columbus, Ohio, US; K. KIMURA et al .: "Ferroelectric properties of vinylidene fluoride-trifluoroethylene copolymer thin films". This copolymer has the particularity of having a phase transition of the ferroelectric type at a temperature higher than ambient temperature and which is a function of the ratio VF2NF3. However, the temperature range where the dielectric constant is high (between 40 and 50) is limited.

Plus récemment sont apparus des terpolymères, par exemple le terpolymère de fluorure de vinylidène, de trifluoroéthylène et d'hexafluoropropène noté P(VF2-TrFE-HFP) ou le terpolymère de fluorure de vinylidène, de tifluoroéthylène et de trifluorochloroéthylène noté P(VF2-TrFE-TrFCIE). Ces terpolymères présentent encore un caractère ferroélectrique mais les transitions à la température de Curie sont diffuses. Il en résulte que le domaine des températures pour lequel le matériau possède une constante diélectrique élevée est élargie par rapport à celui des copolymères, mais encore insuffisamment.More recently, terpolymers have appeared, for example the terpolymer of vinylidene fluoride, trifluoroethylene and hexafluoropropene denoted P (VF 2 -TrFE-HFP) or the terpolymer of vinylidene fluoride, tifluoroethylene and trifluorochloroethylene denoted P (VF 2 -TrFE-TrFCIE). These terpolymers still exhibit a ferroelectric character but the transitions at the Curie temperature are diffuse. As a result, the temperature range for which the material has a high dielectric constant is enlarged compared to that of the copolymers, but still insufficiently.

Afin de pallier ces inconvénients, l'invention propose des alliages de polymères ferroélectriques à températures de Curie différentes, ces alliages permettant d'optimiser les propriétés diélectriques sur une gamme de températures et de fréquences étendue. Ces alliages peuvent être réalisés à base de copolymères, à base d'un homopolymère et d'un ou plusieurs copolymères ou encore à base terpolymères.In order to overcome these drawbacks, the invention provides alloys of ferroelectric polymers at different Curie temperatures, these alloys making it possible to optimize the dielectric properties over a wide range of temperatures and frequencies. These alloys can be produced on the basis of copolymers, on the basis of a homopolymer and on one or more copolymers or else on the basis of terpolymers.

L'invention a donc pour objet un matériau diélectrique à constante diélectrique élevée à base de polymères ferroélectriques de type copolymères et terpolymères de fluorure de vinylidène, caractérisé en ce qu'il est constitué d'un alliage de polymères ferroélectriques à températures de Curie différentes.The subject of the invention is therefore a dielectric material with a high dielectric constant based on ferroelectric polymers of the vinylidene fluoride copolymer and terpolymer type, characterized in that it consists of an alloy of ferroelectric polymers at different Curie temperatures.

Les polymères ferroélectriques peuvent être des copolymères de fluorure de vinylidène et de trifluoroéthylène P(VF2-VF3). L'alliage peut comporter deux ou trois copolymères de ce type.The ferroelectric polymers can be copolymers of vinylidene fluoride and of trifluoroethylene P (VF 2 -VF 3 ). The alloy can comprise two or three copolymers of this type.

L'alliage peut également être réalisé à partir d'un homopolymère tel le PVF2 et d'un copolymère tel le P(VF2-VF3).The alloy can also be produced from a homopolymer such as PVF 2 and a copolymer such as P (VF 2 -VF 3 ).

Les polymères ferroélectriques peuvent être des terpolymères ce qui a l'avantage d'agrandir la zone à constante diélectrique élevée lorsque la température varie.Ferroelectric polymers can be terpolymers, which has the advantage of enlarging the zone with a high dielectric constant when the temperature varies.

Les alliages peuvent être obtenus par mélange de deux terpolymères ou par mélange d'un terpolymère avec un copolymère.The alloys can be obtained by mixing two terpolymers or by mixing a terpolymer with a copolymer.

L'invention sera mieux comprise et d'autres avantages apparaîtront au moyen de la description qui va suivre et des figures annexées parmi lesquelles:

  • - la figure 1 est un diagramme se rapportant à différents polymères de l'art connu,
  • - les figures 2 et 3 sont des diagrammes représentant l'évolution de la constante diélectrique relative en fonction de la température pour des matériaux selon l'invention,
    • la figure 4 est un diagramme représentant le flux de chaleur exothermique pour un matériau selon l'invention,
    • les figures 5 et 7 sont des diagrammes représentant l'évolution de la constante diélectrique avec la température pour des matériaux selon l'invention,
    • la figure 6 est un diagramme illustrant la variation de la constante diélectrique avec la température pour des terpolymères.
The invention will be better understood and other advantages will appear from the following description and the appended figures, among which:
  • FIG. 1 is a diagram relating to various polymers of the known art,
  • FIGS. 2 and 3 are diagrams representing the evolution of the relative dielectric constant as a function of the temperature for materials according to the invention,
    • FIG. 4 is a diagram representing the exothermic heat flow for a material according to the invention,
    • FIGS. 5 and 7 are diagrams representing the evolution of the dielectric constant with the temperature for materials according to the invention,
    • FIG. 6 is a diagram illustrating the variation of the dielectric constant with the temperature for terpolymers.

Dans ce qui suit, le terme polymère sera compris au sens large, c'est-à-dire englobant les copolymères et les terpolymères.In what follows, the term polymer will be understood broadly, that is to say encompassing copolymers and terpolymers.

Les différents alliages seront réalisés par malaxage en phase fondue des différents composants sur un mélangeur à rouleaux chauffants pour une température d'environ 200°C. Les mélanges sont ensuite pressés sous forme de films minces de 100 à 120 µm d'épaisseur par compression à une température d'environ 180°C et refroidis par trempe dans l'eau afin de limiter la cristallisation. Puis les échantillons sont recouverts de métallisations, par exemple en aluminium, sur leurs faces principales afin de pouvoir mesurer leur constante diélectrique Er et leur facteur de perte tg8. Les mesures seront effectuées pour une fréquence de 100 Hz et sur une gamme de température variant de -10°C à 140°C.The various alloys will be produced by mixing in the molten phase of the various components on a mixer with heated rollers for a temperature of approximately 200 ° C. The mixtures are then pressed in the form of thin films from 100 to 120 µm thick by compression at a temperature of around 180 ° C and cooled by quenching in water to limit crystallization. Then the samples are covered with metallizations, for example aluminum, on their main faces in order to be able to measure their dielectric constant E r and their loss factor tg8. The measurements will be made for a frequency of 100 Hz and over a temperature range varying from -10 ° C to 140 ° C.

La figure 1 est un diagramme montrant l'évolution de la constante diélectrique εr en fonction de la température exprimée en degrés Celsius pour différents polymères de l'art connu. Il s'agit de copolymères de fluorure de vinylidène et de trifluoréthylène soit P(VF2-VF3) pour différentes compositions. La courbe 1 se rapporte à un copolymère noté 70/30, c'est-à-dire où la proportion de fluorure de vinylidène intervient pour 70 % en proportion molaire de constituants et le trifluoroéthylène 30 %. La courbe 2 se rapporte au même type de copolymère mais pour une proportion 60/40. De même, la courbe 3 se rapporte à une composition de proportion 50/50. Comme on le distingue très bien sur ce diagramme, ces copolymères présentent une transition de phase de type ferroélectrique à une température supérieure à la température ambiante et qui est fonction des proportions de ses constituants. Cette transition donne lieu à un maximum de la constante diélectrique εr qui est relativement élevée (autour de 40). Cette transition s'accompagne d'un changement de structure cristalline de la phase polaire à la phase non polaire. On admettra que le maximum de constante diélectrique correspond à la temperature de Curie.FIG. 1 is a diagram showing the evolution of the dielectric constant εr as a function of the temperature expressed in degrees Celsius for various polymers of the known art. These are copolymers of vinylidene fluoride and trifluoroethylene, ie P (VF 2 -VF 3 ) for different compositions. Curve 1 relates to a copolymer noted 70/30, that is to say where the proportion of vinylidene fluoride is involved for 70% in molar proportion of constituents and trifluoroethylene 30%. Curve 2 relates to the same type of copolymer but in a 60/40 proportion. Similarly, curve 3 relates to a composition of 50/50 proportion. As can be clearly seen on this diagram, these copolymers exhibit a phase transition of the ferroelectric type at a temperature above ambient temperature and which is a function of the proportions of its constituents. This transition gives rise to a maximum of the dielectric constant εr which is relatively high (around 40). This transition is accompanied by a change in crystal structure from the polar phase to the non-polar phase. It will be assumed that the maximum dielectric constant corresponds to the Curie temperature.

On constate, d'après le diagramme de la figure 1, que le maximum de constante diélectrique se situe à une température relativement élevée (80°C pour la composition 50/50) et que ce maximum n'existe que pour une gamme de températures assez restreinte. La constante diélectrique diminue rapidement lorsque la température passe de la température de Curie à la température ambiante. Par exemple, la composition 60/40 passe d'environ 42 pour 100°C à environ 10 pour 20°CIt can be seen from the diagram in FIG. 1 that the maximum dielectric constant is located at a relatively high temperature (80 ° C. for the 50/50 composition) and that this maximum only exists for a range of temperatures. quite limited. The dielectric constant decreases rapidly when the temperature changes from the Curie temperature to the ambient temperature. For example, the 60/40 composition goes from about 42 for 100 ° C to about 10 for 20 ° C

A titre de comparaison, la courbe 4 représente la variation de sr en fonction de la température dans le cas du polyfluorure de vinylidène. On constate donc qu'il est possible d'accroître sensiblement la constante diélectrique grâce aux copolymères mais pour des températures élevées et pour des gammes de températures restreintes.By way of comparison, curve 4 represents the variation of sr as a function of the temperature in the case of polyvinylidene fluoride. It is therefore found that it is possible to substantially increase the dielectric constant thanks to the copolymers but for high temperatures and for restricted temperature ranges.

La figure 2 est un diagramme représentant la variation de la constante diélectrique εr avec la température pour des alliages selon l'invention. Il s'agit d'alliages entre des copolymères de fluorure de vinylidène et de trifluoroéthylène de concentration différentes. L'alliage A, correspondant à la courbe 5 , contient 50% en poids d'une composition 60/40 et 50% d'une composition 70/30. Cet alliage présente un plateau dans le comportement diélectrique avec er de l'ordre de 40 à partir de 110°C alors que cette valeur n'est que de 10 à 25°C. L'amplitude du plateau ne varie que de quelques unités dans une gamme de températures d'une quarantaine de degrés. C'est une caractéristique intéressante bien que le plateau se présente à des températures relativement élevées.FIG. 2 is a diagram representing the variation of the dielectric constant εr with the temperature for alloys according to the invention. These are alloys between copolymers of vinylidene fluoride and trifluoroethylene of different concentrations. Alloy A, corresponding to curve 5, contains 50% by weight of a 60/40 composition and 50% of a 70/30 composition. This alloy has a plateau in dielectric behavior with er of the order of 40 from 110 ° C while this value is only from 10 to 25 ° C. The amplitude of the plateau varies only by a few units in a range of temperatures of around forty degrees. This is an interesting characteristic although the plateau occurs at relatively high temperatures.

L'alliage B, correspondant à la courbe 6, contient 70 % en poids d'une composition 50/50 et 30 % d'une composition 60/40. Cet alliage présente, autour de 70°C, un maximum de 45 pour er. La constante diminue ensuite jusqu'à 30 pour une température de l'ordre de 120°C. La constante diélectrique maximale est élevée pour une température moyenne mais le plateau est encore assez étroit.Alloy B, corresponding to curve 6, contains 70% by weight of a 50/50 composition and 30% of a 60/40 composition. This alloy has, around 70 ° C, a maximum of 45 to er. The constant then decreases to 30 for a temperature of the order of 120 ° C. The maximum dielectric constant is high for an average temperature but the plate is still quite narrow.

Pour ces alliages, le facteur de perte est inférieur à 0,03 jusqu'à 90°C.For these alloys, the loss factor is less than 0.03 up to 90 ° C.

La figure 3 est un diagramme représentant la variation de la constante diélectrique er avec la température pour d'autres alliages selon l'invention. Il s'agit d'alliages réalisés à partir de trois copolymères de fluorure de vinylidène et de trifluorure d'éthylène de compositions 50/50, 60/40 et 70/30 pris en proportions différentes.FIG. 3 is a diagram representing the variation of the dielectric constant er with the temperature for other alloys according to the invention. These are alloys produced from three copolymers of vinylidene fluoride and ethylene trifluoride of compositions 50/50, 60/40 and 70/30 taken in different proportions.

L'alliage C, correspondant à la courbe 7, présente une proportion en poids égale pour les trois compositions. L'alliage D, correspondant à la courbe 8 présente une proportion en poids de 45 % pour la composition 50/50, 35% pour la composition 60/40 et 20 % pour la composition 70/30. On note, pour les deux mélanges, la présence d'un plateau débutant aux environs de la température de Curie de la composition 50/50 soit 75°C. Pour l'alliage C, le plateau a une valeur assez constante (εr entre 35 et 40) pour une large gamme de températures (entre 75 et 140°C). C'est le faible pourcentage de la composition 70/30 dans l'alliage D (voir la courbe 8) qui entraîne une baisse de la constante diélectrique pour les températures supérieures à 105°C.Alloy C, corresponding to curve 7, has an equal proportion by weight for the three compositions. Alloy D, corresponding to curve 8, has a proportion by weight of 45% for the composition 50/50, 35% for the composition 60/40 and 20% for the composition 70/30. We note, for the two mixtures, the presence of a plateau starting at around the Curie temperature of the composition 50/50, ie 75 ° C. For alloy C, the plateau has a fairly constant value (εr between 35 and 40) for a wide range of temperatures (between 75 and 140 ° C). It is the low percentage of the composition 70/30 in the alloy D (see curve 8) which causes a drop in the dielectric constant for temperatures above 105 ° C.

Pour ce type d'alliages, les pertes diélectriques sont inférieures à 0,04 jusqu'à 110°C.For this type of alloy, the dielectric losses are less than 0.04 up to 110 ° C.

La figure 4 est un diagramme représentant le flux de chaleur exothermique FCE pour l'alliage C. La courbe 9 représente la variation de constante diélectrique sr en fonction de la température. Elle correspond à la courbe 7 de la figure 3. La courbe 10 représente le flux de chaleur exothermique de cet alliage en fonction de la température. La mesure de ce flux de chaleur a été effectuée par analyse thermique différentielle ou DSC d'après la terminologie anglo-saxonne (Différential Scanning Calorimetry). La courbe 10 présente, pour la gamme de température correspondant au plateau de la courbe 9, un creux où l'on peut relever plusieurs températures significatives. On relève ainsi les trois températures Tci, Tc2 et Tc3. Les deux premières sont bien visibles sur la courbe 10 puisqu'elles correspondent à des minimums de flux de chaleur. La troisième correspond à un point d'inflexion de la courbe 10. L'intérêt de cette courbe est qu'elle illustre bien le fait que le mélange de plusieurs copolymères ferroélectriques à températures de Curie différents donne un alliage dont la transition de Curie est une combinaison des différentes transitions de Curie. On remarque l'étalement de la transition comprise entre Tci (environ 75°C) et Tc3 (environ 105°C). Tci correspond à la température de Curie de la composition 50/50 et Tc3 à la température de Curie de la composition 70/30. Tc2 correspond à la température de Curie de la composition 60/40. On peut prévoir ainsi que la largeur du plateau à constante diélectrique sensiblement constante avec la température dépendra de la différence plus ou moins grande existant entre les températures de Curie des différentes compositions. Pour que le plateau se rapproche de la température ambiante, il faudra donc que la température de Curie de l'un des constituants s'en rapproche.FIG. 4 is a diagram representing the exothermic heat flow FCE for the alloy C. The curve 9 represents the variation of dielectric constant sr as a function of the temperature. It corresponds to curve 7 in FIG. 3. Curve 10 represents the exothermic heat flow of this alloy as a function of the temperature. The measurement of this heat flux was carried out by differential thermal analysis or DSC according to Anglo-Saxon terminology (Differential Scanning Calorimetry). Curve 10 presents, for the temperature range corresponding to the plateau of curve 9, a trough where several significant temperatures can be noted. The three temperatures Tc i , Tc 2 and Tc 3 are thus noted. The first two are clearly visible on curve 10 since they correspond to minimum heat fluxes. The third corresponds to an inflection point on curve 10. The advantage of this curve is that it illustrates well the fact that the mixture of several ferroelectric copolymers at different Curie temperatures gives an alloy of which the Curie transition is a combination of the different Curie transitions. Note the spread of the transition between Tci (approximately 75 ° C) and Tc 3 (approximately 105 ° C). Tc i corresponds to the Curie temperature of the composition 50/50 and Tc3 corresponds to the Curie temperature of the composition 70/30. Tc 2 corresponds to the Curie temperature of the composition 60/40. So we can plan that the width of the plate with a dielectric constant which is substantially constant with the temperature will depend on the greater or lesser difference between the Curie temperatures of the different compositions. So that the plateau approaches the ambient temperature, it will therefore be necessary for the Curie temperature of one of the constituents to approach it.

La figure 5 est un diagramme représentant la variation de la constante diélectrique er avec la température pour d'autres alliages selon l'invention. Il s'agit d'alliages réalisés à partir de l'homopolymère PVF2 et de copolymères de fluorure de vinylidène et de trifluoroéthylène. On peut représenter ces alliages par la notation : PVF2 + P(VF2NF3). Le type de copolymère (60/40 ou 70/30 par exemple) employé dans le mélange est déterminant pour le positionnement en température du plateau et pour la valeur de er sur ce plateau. Ainsi sur la figure 5, le maximum de constante diélectrique (Er=30) est observé à partir de 80°C pour l'alliage E contenant 40% en poids de PVF2 pour 60 % d'un copolymère 60/40. L'alliage E est représenté à la figure 5 par la courbe 11.FIG. 5 is a diagram representing the variation of the dielectric constant er with the temperature for other alloys according to the invention. These are alloys made from the PVF 2 homopolymer and copolymers of vinylidene fluoride and trifluoroethylene. These alloys can be represented by the notation: PVF 2 + P (VF 2 NF 3 ). The type of copolymer (60/40 or 70/30 for example) used in the mixture is decisive for the temperature positioning of the plate and for the value of er on this plate. Thus in FIG. 5, the maximum dielectric constant ( E r = 3 0) is observed from 80 ° C. for the alloy E containing 40% by weight of PVF 2 for 60% of a 60/40 copolymer. The alloy E is represented in FIG. 5 by curve 11.

L'alliage F composé de 60 % en poids de PVF2 et de 40% d'un copolymère 70/30 présente un maxima de constante diélectrique (environ 30) à partir de 110°C (voir la courbe12).Alloy F composed of 60% by weight of PVF 2 and 40% of a 70/30 copolymer has a maximum dielectric constant (around 30) from 110 ° C (see curve 12).

La diffraction de rayons X sur ces mélanges ne montre pas de cristallisation en phase p du PVF2 mais une cristallisation en phase α, phase thermo- dynamiquement la plus stable.X-ray diffraction on these mixtures does not show p-phase crystallization of PVF 2, but crystallization in α-phase, the thermodynamically most stable phase.

La figure 6 est un diagramme représentant la variation de la constante électrique εr avec la température dans le cas de terpolymères. La courbe 13 est relative à un terpolymère Ti de trifluoroéthylène, de fluorure de vinylidène et d'hexafluoropropè- ne HFP que l'on notera P(VF3 - VF2 - HFP) et dont les proportions en moles dans le mélange sont respectivement 35, 60 et 5 %. Les courbes 14 et 15 sont relatives à des terpolymères (respectivement T2 et Ts) de trifluoroéthylène, de fluorure de vinylidène et de trifluorochloroéthylène que l'on notera P(VF3 - VF2 - TrFCIE). Pour la courbe 14, les proportions en moles des parties dans le mélange sont respectivement de 35, 60 et 5 %. Pour la courbe 15, les proportions en moles sont respectivement de 35, 55 et 10 %. On constate que pour ces terpolymères, les maximums de sr correspondent à des températures plus basses que pour les copolymères de la figure 1 et pour des valeurs de εr de même ordre de grandeur. On constate malheureusement l'absence de plateau comme pour les copolymères.FIG. 6 is a diagram representing the variation of the electrical constant εr with the temperature in the case of terpolymers. Curve 13 relates to a terpolymer T i of trifluoroethylene, vinylidene fluoride and hexafluoropropene HFP which will be denoted P (VF 3 - VF 2 - HFP) and the proportions of which in moles in the mixture are respectively 35, 60 and 5%. Curves 14 and 15 relate to terpolymers (respectively T 2 and Ts) of trifluoroethylene, vinylidene fluoride and trifluorochloroethylene which will be denoted P (VF 3 - VF 2 - TrFCIE). For curve 14, the proportions in moles of the parts in the mixture are respectively 35, 60 and 5%. For curve 15, the proportions in moles are respectively 35, 55 and 10%. It can be seen that for these terpolymers, the maximums of sr correspond to lower temperatures than for the copolymers of FIG. 1 and for values of εr of the same order of magnitude. Unfortunately, there is an absence of a plateau as for the copolymers.

La figure 7 est un diagramme représentant la variation de la constante diélectrique er avec la température dans le cas d'alliages de terpolymères entre eux ou avec un copolymère. La courbe 16 se rapport à un alliage G formé de 30 % en poids de Ti et de 70% de Ts. L'alliage G présente un maximum de constante diélectrique (εr = 35) autour de 55°C à la température de Curie observée sur le terpolymère T3 seul. On notera cependant la valeur élevée de er (environ 20) pour la température de 20°C.FIG. 7 is a diagram representing the variation of the dielectric constant er with the temperature in the case of alloys of terpolymers together or with a copolymer. Curve 16 relates to an alloy G formed of 30% by weight of Ti and 70% of Ts. Alloy G has a maximum dielectric constant (εr = 35) around 55 ° C at the Curie temperature observed on the T 3 terpolymer alone. Note however the high value of er (around 20) for the temperature of 20 ° C.

L'alliage H est formé de 30% en poids de Ti et de 70 % de T2 et correspond à la courbe 17. Cette courbe présente un plateau étendu en température (entre 60 et 130°C), de valeur élevée et relativement constante (Er de 45 à 50). Dans ces conditions, cet alliage est particulièrement intéressant.Alloy H is formed by 30% by weight of T i and 70% by T 2 and corresponds to curve 17. This curve has an extended temperature plateau (between 60 and 130 ° C), of high value and relatively constant ( E r from 45 to 50). Under these conditions, this alloy is particularly advantageous.

L'alliage est formé de 70 % en poids de terpolymère T3 et de 30 % de copolymère VF2 - VFs de proportions 60/40 (60 % en poids de VF2 pour 40 % en poids de VFs). Cette alliage correspond à la courbe 18. Cette courbe ne présente pas de plateau étendu mais l'alliage I permet l'obtention d'un matériau de constante diélectrique comprise entre 20 et 30 pour une gamme de températures s'étalant de 20 à 100°C et dont le maximum se situe autour de 80°C.The alloy is formed from 70% by weight of terpolymer T 3 and 30% of copolymer VF 2 - VFs of proportions 60/40 (60% by weight of VF 2 for 40% by weight of VF s ). This alloy corresponds to curve 18. This curve does not have an extended plateau, but alloy I makes it possible to obtain a material with a dielectric constant of between 20 and 30 for a range of temperatures ranging from 20 to 100 °. C and the maximum of which is around 80 ° C.

La présente invention ne se limite pas aux exemples cités plus haut. Elle s'applique à tous les alliages de polymères ferroélectriques.The present invention is not limited to the examples cited above. It applies to all ferroelectric polymer alloys.

D'autre part, il entre dans le cadre de l'invention d'utiliser ces matériaux pour d'autres applications. Par polarisation contrôlée, ils peuvent acquérir des propriétés piézoélectriques ou pyroélectriques caractéristiques des ferroélectriques à transistions diffuses.On the other hand, it is within the scope of the invention to use these materials for other applications. By controlled polarization, they can acquire piezoelectric or pyroelectric properties characteristic of ferroelectrics with diffuse transistions.

Claims (13)

1. A dielectric material having a high dielectric constant, basically constituted of ferroelectric polymers of the vinylidene fluoride copolymeric and terpolymeric type, characterized in that it is constituted of an alloy of ferroelectric polymers having different Curie temperatures.
2. A dielectric material according to claim 1, characterized in that said ferroelectric polymers are copolymers of vinylidene fluoride and of trifluoroethylene.
3. A dielectric material according to claim 2, characterized in that the alloy is constituted by 50% by weight of a copolymer comprising 60 Mol% of vinylidene fluoride and 40 Mol% of trifluoroethylene, and by 50% by weight of a copolymer comprising 70 Mol% of vinylidene fluoride and 30 Mol% of tri- fluororethylene.
4. A dielectric material according to claim 2, characterized in that the alloy is constituted by 30% by weight of a copolymer comprising 60 Mol% of vinylidene fluoride and 40 Mol% of trifluoroethylene, and by 70% by weight of a copolymer comprising 50 Mol% of vinylidene fluoride and 50 Mol% of tri- fluororethylene.
5. A dielectric material according to claim 2, characterized in that the alloy is constituted by one third by weight of a copolymer comprising 50 Mol% of vinylidene fluoride and 50 Mol% of trifluoroethylene, by one third by weight of a copolymer comprising 60 Mol% of vinylidene fluoride and 40 Mol% of tri- fluororethylene, and by one third by weight of a copolymer comprising 70 Mol% of vinylidene fluoride and 30 Mol% of trifluoroethylene.
6. A dielectric material according to claim 2, characterized in that the alloy is constituted by 45% by weight of a copolymer comprising 50 Mol% of vinylidene fluoride and 50 Mol% of trifluoroethylene, by 35% by weight of a copolymer comprising 60 Mol% of vinylidene fluoride and 40 Mol% of trifluoror- ethylene and by 20% by weight of a copolymer comprising 70 Mol% of vinylidene fluoride and 30 Mol% of trifluoroethylene.
7. A dielectric material according to claim 1, characterized in that the ferroelectric polymers are the polyfluoride of vinylidene (PVF2) and the copolymer of vinylidene fluoride and of trifluoroethylene.
8. A dielectric material according to claim 7, characterized in that the alloy is constituted by 40% by weight of PVF2 and by 60% of a copolymer comprising 60 Mol% of vinylidene fluoride and 40 Mol% of trifluoroethylene.
9. A dielectric material according to claim 7, characterized in that the alloy is constituted by 60% by weight of PVF2 and by 40% of a copolymer comprising 70 Mol% of vinylidene fluoride and 30 Mol% of trifluoroethylene.
10. A dielectric material according to claim 1, characterized in that the ferroelectric polymers comprise at least one terpolymer.
11. A dielectric material according to claim 10, characterized in that the alloy is constituted by 30% by weight of a terpolymer comprising 35 Mol% of trifluoroethylene, 60 Mol% of vinylidene fluoride and 5 Mol% of hexafluoropropene, and by 70% by weight of a terpolymer comprising 35 Mol% of trifluoroethylene, 55 Mol% of vinylidene fluoride and 10 Mol% of trifluorochloroethylene.
12. A dielectric material according to claim 10, characterized in that the alloy is constituted by 30% by weight of a terpolymer comprising 35 Mol% of trifluoroethylene, 60 Mol% of vinylidene fluoride and 5 Mol% of hexafluoropropene, and by 75% by weight of a terpolymer comprising 35 Mol% of trifluoroethylene, 60 Mol% of vinylidene fluoride and 5 Mol% of trifluorochloroethylene.
13. A dielectric material according to claim 10, characterized in that the alloy is constituted by 70% by weight of a terpolymer comprising 35 Mol% of trifluoroethylene, 55 Mol% of vinylidene fluoride and 10 Mol% of hexafluoropropene, and by 30% by weight of a copolymer comprising 60 Mol% of vinylidene fluoride and 40 Mol% of trifluoroethylene.
EP86401317A 1985-06-21 1986-06-17 Polymeric dielectric material with a high dielectric permittivity Expired EP0206926B1 (en)

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